Activation of the CKI-CDK-Rb-E2F Pathway in Full Genome Hepatitis C Virus-expressing Cells

Hepatitis C virus (HCV) causes persistent infection in hepatocytes, and this infection is, in turn, strongly associated with the development of hepatocellular carcinoma. To clarify the mechanisms underlying these effects, we established a Cre/loxP conditional expression system for the precisely self-trimmed HCV genome in human liver cells. Passage of hepatocytes expressing replicable full-length HCV (HCR6-Rz) RNA caused up-regulation of anchorage-independent growth after 44 days. In contrast, hepatocytes expressing HCV structural, nonstructural, or all viral proteins showed no significant changes after passage for 44 days. Only cells expressing HCR6-Rz passaged for 44 days displayed acceleration of CDK activity, hyperphosphorylation of Rb, and E2F activation. These results demonstrate that full genome HCV expression up-regulates the CDK-Rb-E2F pathway much more effectively than HCV proteins during passage

Transcriptional regulation of indoleamine 2,3-dioxygenase (IDO) by tryptophan and its analogue: Down-regulation of the indoleamine 2,3-dioxygenase (IDO) transcription by tryptophan and its analogue

Indoleamine 2,3-dioxygenase (IDO; EC 1.13.11.42) is a rate-limiting enzyme involved in the catabolism of tryptophan, which is an essential amino acid. It is induced under pathological conditions, such as the presence of viral infections or tumour cells. This enzyme is induced by IFN-γ in the mouse rectal carcinoma cell line CMT-93. It is known that both 1-methyl-l-tryptophan (1-MT) and methylthiohydantoin-dl-tryptophan (MTH-trp) are tryptophan analogues, and are authentic inhibitors of the enzymatic activity of IDO. In this study, we examined the effects of both 1-MT and MTH-trp on the IFN-γ inducible IDO expression of CMT-93. As a result, the IFN-γ inducible IDO mRNA and the protein levels in CMT-93 were suppressed by 1-MT and MTH-trp, independently. Moreover, tryptophan (Trp), as a substrate of IDO, also suppressed IDO induction by IFN-γ at the transcriptional level. These results suggest that 1-MT and MTH-trp are as inhibitors of IDO enzymatic activity, and Trp suppresses IDO induction by IFN-γ at the transcriptional level